Personally, yeah it'd be fine. Turn ins would be the same to be as trading away the rights to the character if I were to trade or sell it

The person who now has the character can do whatever they please with it (as long as it follows any additional CS based rules, but I no longer have even a fraction of a say in what happens once something leaves my hands)

I can't see a lot of "nos", but if there are, you could just have the option of if the original designer was not present for the turn in, have some be trade and have those that were from/got explicit consent from the og designer allow monetary value?

Probably a bit of a complex process, but some people get very sensitive about things they don't own on this site LOL

Oop edit: if I handed something in you liked but didn't edit much, I would just consider you reselling it, which since you're the owner of the species you'd be well within you're right to do, since IIRC you do tend to at least create new artwork for the revamped designs, so mightspeed!